These Northern Lights “rainbows” have turned the sky greener than the Earth below. Vitaly Istomin, 26, spent several nights in freezing conditions under the stars in northern Russia’s Khibiny Mountains to capture the aurora’s “rainbows”. (Photo by Vitaly Istomin/Caters News Agency)

Somali couple Mohamed Noor (L) and Huda Omar pose for a photograph at their makeshift home during their wedding ceremony in Mogadishu's Rajo camp, Somalia August 17, 2016. Having met two years ago, the pair have just married at Rajo camp, where some 400 families live. Most, like Noor's parents, came here in the early 1990s to flee famine. (Photo by Feisal Omar/Reuters)

Everyone wants to get something for nothing - whether it's a lucky upgrade that means you can turn left when you get on a plane instead or heading off into the economy seats, or even getting a few extra features thrown in for free when you buy a new car.

As some of the sharpest businesses around, no-one understands this quite as well as casinos and that's why they all have a system that they call comps. It's short for "complimentary offers" and these are special treats specially designed to reward you for your loyalty to the casino in question. They're basically bonuses.

A paper rhacophorus arvalis (farmland green tree frog) of Taiwan (R) is surrounded by paper pandas at an exhibition called “Pandas on Tour” at the National Theater in Taipei on February 24, 2014. Some 1,600 paper made pandas are on display, designed by French artist Paulo Grangeon. (Photo by Mandy Cheng/AFP Photo)

Children play with toy guns during Eid al-Fitr celebrations in Peshawar, Pakistan, 24 May 2020. Muslims around the world are celebrating Eid al-Fitr, the three day festival marking the end of the Muslim holy fasting month of Ramadan. Eid al-Fitr is one of the two major holidays in Islam. (Photo by Bilawal Arbab/EPA/EFE/Rex Features/Shutterstock)

A disabled child is buried up to his neck in sand during the partial solar eclipse in belief its rays can heal, in Karachi, Pakistan, 25 October 202. A partial solar eclipse occurs when a portion of the Earth is engulfed by the shadow (penumbra) cast by the Moon as it passes between our planet and the Sun in imperfect alignment. During this eclipse - the first of the decade – the Moon appears to cover the Sun, leaving the Sun's halo as a visible rim forming an annulus, popularly known as the 'ring of fire. (Photo by Shahzaib Akber/EPA/EFE/Rex Features/Shutterstock)

Pod of dolphins surf effortlessly through the waves in the wild traveling at speeds up to 20 mph. (Photo by Greg Huglin)

Inspired by traditional Indian travelling photography studios, Arthur Crestani photographed the inhabitants of Gurgaon, a city built almost entirely by private companies. Arthur Crestani’s “Bad City Dreams” contrasts the glossy ideal sold by developers with urban reality. Here: Luxury Living Bhiwadi: “Sky Club on 18th Floor”. (Photo by Arthur Crestani/The Guardian)